Windows only: Virtual desktop utility DoubleDesktop does exactly what its name implies—it creates two virtual desktops in a tiny package that uses less than 1 MB of RAM.

Using the lightweight utility is very simple—just click the system tray icon to switch back and forth between the two virtual desktops, or optionally set a hotkey in the preferences to flip between the two virtual desktops. Moving windows between desktops is the only annoying part—you have to drag them halfway and catch them on the other side.